Right-handed pitcher Aaron Cook, who was supposed to start Thursday night's game against the Padres, was off in the training room being treated for a strained oblique muscle. He'll have plenty of time, since the club was to place him on the 15-day disabled list after Wednesday night's game.
The Rockies wanted Dessens, 36, before the 2006 season, but he signed with the Royals, who later traded him to the Dodgers. This year, Dessens was available when the Rockies need him.
Dessens signed with the Brewers during the offseason, but he was released in August after the club obtained reliever Scott Linebrink from the Padres. Before the Brewers let him go, they had placed him on the disabled list with a shoulder strain and had him make three injury rehab appearances for Triple-A Nashville.
On Friday, Dessens signed a Minor League contract with the Rockies and pitched that night at Triple-A Colorado Springs, giving up one hit, walking one and striking out one in three innings of a 9-5 victory over Tacoma.
"When I left Milwaukee, I still felt pretty good," Dessens said. "I am able to still pitch in the big leagues. I signed here in Colorado, and they're going to give me the opportunity to help the team win some games.
"I've kept in mind that this team was interested in me. I talked to my agent, and we were watching this team play and saw an opportunity."
It will be Dessens' first start since Oct. 2, 2005, a loss to the Padres at PETCO Park in the final regular-season game. Dessens is 0-3 with a 4.72 ERA in seven games at PETCO, including two starts.
Pain remained: Cook suffered the oblique strain during his last start, a loss at home to the Cubs. Cook went six innings and seemed fine immediately thereafter, but he could not fully recover.
"Once I took him out, he was good with it, and a couple days later he was real good with hit," manager Clint Hurdle said. "Then we tried to see where we could go from there.
"He hasn't been able to get in the work he needed to get in or even feel he would be ready to take the ball again -- on time or even with a short delay."
A chance earned: With center fielder Willy Taveras on the 15-day disabled list with his troublesome right quadriceps (righty reliever Ramon Ramirez was called up to take his place), Ryan Spilborghs will get his first chance at regular duty in center.
Spilborghs entered his start Wednesday against the Padres batting .331 with 10 home runs and 43 RBIs in 59 games after being called up from Triple-A Colorado Springs. Also with the Rockies are one-time starting center fielder Cory Sullivan, who has value as a left-handed hitter off the bench, and right-handed hitting utility man Clint Barmes.
"'Spilly' will get every opportunity to go out there," Hurdle said. "Then we're going to look at the best fit afterward, whether it's matchup or what have you. I'm going to run Barmes out there a couple of times because I want to. I think he might be a fit.
"It might be a two-headed monster or a three-headed monster; I don't know. We'll have somebody playing center field who will man the position very well."
Pain-free: Lefty reliever Brian Fuentes faced four hitters in Tuesday's 8-0 loss to the Padres, striking out two, walking one and giving up a hit, in his return from missing more than a month with a strained lat muscle. He reported no pain, but admitted he wasn't fully sharp.
"Physically, I felt fine, felt normal," said Fuentes, who said he was surprised how long it took for the strain to heal. "I think I was just a tick off mechanically. I threw a few more pitches  than I wanted to throw."
Fuentes is pitching in a setup role and won't be considered to be restored to closing games at least until he can pitch on back-to-back days. Hurdle said Fuentes is not at that point and would not be used Wednesday.
Fuentes earned three All-Star invitations as a closer, but he slumped before the injury and Manny Corpas went 9-for-9 in save chances in his absence. Fuentes said now, with the Rockies still with legitimate playoff hopes, is not the time to campaign for his usual role.
"I'm just trying to help the team out, whether it's the sixth inning or the ninth inning, whatever they want me to do," he said. "Obviously, I still want to close, here or somewhere else or wherever. But right now, I'm just concerned with getting back out and putting up scoreless innings.
"I want to close, but if Manny's doing the job well and he's closing, I want to get him to that ninth inning. It's about winning right now. We're at a point in the season where we can't afford anybody to be selfish."
Getting those signatures in early: The deadline for clubs to sign players from the First Year Player Draft, and not lose their rights, was Wednesday at 10 p.m. MT. Some teams were to the wire with top picks, but the Rockies had signed their top 13 choices. The last of the high picks to sign, fifth-rounder Connor Graham, a right-hander from Miami (Ohio) University, did so on July 16.
Up next: Dessens, who went 1-1 with a 6.60 ERA in 12 relief appearances with the Brewers before being released, will join the Rockies and start against Padres right-hander Clay Hensley (1-3, 6.18 ERA) Thursday night at 8:05 MT.
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.